In the field of electronics a common desire is to provide a group of signals to a processing circuit while maintaining electrical isolation between the circuit or circuits in which those signals were generated and the processing circuitry. A typical example of a situation where such a desire would arise is when signals from a group of sensors, operating in a relatively higher voltage range, are to be processed by a circuit which operates in a lower voltage range. Those skilled in the art will readily see other situations in electronics where similar isolation is desirable.
Typically in the prior art when such isolation was desired in the context of integrated circuits it was provided either externally to those integrated circuits, by the use of a transformer arrangement, or by the use of an optical system. Transformers are typically rather bulky devices when compared with other electronic components typically associated with integrated circuits. Therefore, transformers are provided external to an integrated circuit chip. Isolation by use of optical techniques is accomplished by modulation of the signal emitted by an optically emitting device, such as a light emitting diode, by the signal to be transferred. The emitter used in such a system is positioned so that the radiation thus emitted strikes a detector. The output of this detector may then be transferred to processing circuitry. Because it is difficult to prevent radiation emitted by one emitter from striking all detectors located on a single monolithic integrated circuit chip, typically only one such detector, and hence only one isolation device, may be provided on a single chip.